(1) Field of the Invention
The invention relates to the field of rotary wing aircraft (e.g. helicopters, rotorcraft, etc.). It relates more particularly to so-called “hybrid” modes of driving the rotation of at least one rotor via a gearbox of the aircraft.
(2) Description of Related Art
As in the automobile field, a power plant is said herein to be “hybrid” when it is possible to obtain mechanical power by selecting between a combustion source, an electrical source, or both sources together.
Although in practice no hybrid helicopters are presently being mass-produced, numerous types of rotary wing aircraft may be concerned by the invention.
A rotary wing aircraft of the invention may include one or more lift rotors referred to as “main” rotors and/or one or more auxiliary rotors.
The term “auxiliary” rotor is used, for example, to designate antitorque rotors (often tail rotors), or propulsion rotors as in a lateral arrangement of propellers on a long-range high-speed helicopter (e.g. see the documents mentioned below).
In most rotary wing aircraft, a rotor is driven via a gearbox. For example, a lift rotor is often driven via a main gearbox (MGB). Certain auxiliary rotors, such as an antitorque rotor, are generally driven by means of a tail gearbox (TGB).
Various known documents are mentioned below.
Documents relating to laterally-arranged propulsion rotors for long-range high-speed helicopters are the following: FR 2 929 243; FR 2 916 418; FR 2 916 419; and FR 2 916 420.
Document US 2009/0145998 describes a vehicle that incorporates gas-turbine and electrical hybrid propulsion. Its FIGS. 2A or 2B show an application to a helicopter. That document does not describe an aircraft in which a combustion engine is coupled mechanically via a transmission to a rotor and where two electricity networks are connected together via a selective adaptation interface.
Document DE 102008014404 describes a hybrid-drive aircraft, e.g. a helicopter drone. A turbine drives a generator and its electricity powers an electric motor and/or charges batteries. The electric motor is caused to operate with electricity from the batteries in an emergency in the event of the turbine failing.
Document U.S. Pat. No. 4,380,725 describes a direct current (DC) power supply from batteries, which power supply includes a plurality of subsystems, each of which includes a temperature sensor. A BTC connector connects together two link buses of the subsystems. The output voltage from each generator is regulated as a function of temperature rises measured by the sensors.
Furthermore, document US 2009/140095, which describes drive via a gearbox, differs from the invention by arrangements in which an electric motor on its own drives a main rotor in all situations, and is incorporated directly in the rotary mast of the rotor.
French patent application No. 09/05678 (now published as FR 2 952 907) describes a rotary wing aircraft having “hybrid drive modes”, e.g. a hybrid power plant implemented on a helicopter. In order to assist or replace drive produced by a combustion engine, that hybrid helicopter power plant includes an electric motor mechanically connected like the combustion engine to the gearbox in order to drive a rotor.
That electric motor is conventionally a brushless motor dimensioned as a function of the first maximum power to be delivered. Furthermore, that electric motor is capable of operating in generator mode and, where necessary, can be used as a brake for the gearboxes. Means for disconnecting the main batteries can be actuated by the pilot in order to activate or stop the electric motors. Those motors, a set of batteries, and a regulator member are independent of the other equipment of the helicopter, in particular its engine and its electricity network.
According to that invention, modes for driving one or more rotors in rotation are of the “hybrid” type in that they associate one or more combustion engine(s) (e.g. a turboshaft engine and/or a piston engine, e.g. a diesel engine) with one or more electrical machines for providing drive. It should be emphasized that such combustion engines and electrical machines are respectively engaged with a transmission (main gearbox (MGB), tail gearbox (TGB), etc.), the transmission being between them and the rotor. In other words, the drive makes use of one or more mechanical drive systems referred to generically as “transmissions”.
In order to illustrate that which is referred to as an “electrical architecture”, mention is made of document FR 2 526 380, which describes producing and delivering electricity for a helicopter, and in particular it describes what may be referred to as an “electrical master box”. In that document, primary contactors and circuit breakers are arranged between the master box, relay boxes, electronic cabinets, and (analog and/or digital) control panels. The master box forms a central unit that also groups together various protection or safety devices.
Other documents are mentioned by way of technological background.
The Document DE 102008014404 describes a helicopter drone that possesses a turbine-driven generator suitable for producing electricity that is delivered to a motor or to batteries for powering said motor. That document describes what might be referred to as a series (or serial) hybrid architecture, i.e. a combustion engine delivering power to rotors via a generator and then, in series, an electric motor. A battery is interposed as a buffer.
Document FR 2 909 233 is an example of an electric starter suitable for operating in synchronous generator mode in a rotorcraft in order to mitigate the fact that an engine is generally overdimensioned. One or more electric motors are engaged with a gearbox and can be used as substitutes for the starter in generator mode. In addition, the electric motors are used to power the low-voltage energy reserve and on-board equipment, via a low-voltage on-board electricity network.
Document US 2009145998 describes (in particular in its FIG. 8B) a two-rotor aircraft having turbines that constitute a first source of drive power. Coupling to one or even three alternating current (AC) electric motors is possible. A clutch is interposed so that the turbine power plant and an electricity generator that is distinct from the electric motors can be selectively engaged or disengaged.
That said, various problems on which the invention is based are explained.
One of these problems stems from the practical difficulty of being able to propose an electrical architecture that is light in weight, reliable, and suitable for hybrid drive, on numerous aircraft models. This should be possible without complicating or increasing the weight of the surrounding electrical architecture (when adding hybrid drive).
This is that much more difficult when for a given aircraft it is desired that hybrid drive should be available as an option. It would then be desirable for the architecture to be completely modular.
Such a variety of configurations thus reduces options for making architectures and their components more uniform between models of a given range of aircraft and between different ranges from the same manufacturer.
According to the invention, “segregation” is made possible between the main electricity network and the auxiliary electricity network used for hybrid drive, the design of the associated electrical architectures thus being greatly simplified and the aircraft potentially being made lighter in overall weight for given mission profile.
It is also appropriate for a suitable quantity of energy to be available on board the aircraft at the required moments and in renewable manner. However, technological, economic, and environment constraints (weight, safety, regulations, . . . ) may conflict with having any guarantee of the electrical architecture being capable of providing the necessary energy distribution and recharging.
All of those problems are made more critical when the aircraft needs to incorporate additional functions that consume large amounts of energy, such as de-icing, winching, ventilation, and air conditioning.
Nevertheless, it is appropriate to avoid overloading the gas generator of its turbine engine when such a member is coupled to the main drive system.
For given overall mission profile, it would also be desirable to be able to achieve energy savings, in particular because of ecological implications and new regulations.
In another register, it is known that certain territories have restricting regulations concerning overflight by single-engined rotary wing aircraft. According to known documents, electrical architectures for power plants (single main engine and auxiliary motor) are interdependent and therefore provide no solution that is acceptable in practice in this field.
Another problem is associated with the fact that demand is increasing for additional and sophisticated items of on-board equipment (de-icing, winching, fans, air conditioning, etc.). The on-board weight of an aircraft is thus tending to increase, and this can even happen during its lifetime. From this point of view, in spite of equipment being optimized, the draconian steps taken to reduce weight can, in practice, constitute an obstacle to providing hybrid drive.
A fortiori, adding hybrid drive as an option or as standard (including functional structures that may represent a weight of the order of several tens of kilograms, i.e. more than the weight of all of the other electricity generator structures), is contradictory and may even be impossible if a model of aircraft is already close to its authorized weight limit.
In conclusion, it can be understood that it is not easy to design, adapt, and produce a hybrid power plant and its architecture so as to have an impact that is favorable in terms of performance (in particular for a multi-engined aircraft such as a twin-engined aircraft), or in terms of safety (in particular for an aircraft having a single engine).
The invention seeks to solve these various problems in particular.